I have absolutely no idea how to include correct alt and src values... just followed the instructions in the “A basic Sigil tutorial”. The cover shows up perfectly, and all is working well, but Threepress gave the above error. I tried changing some of the names of the image etc, but got nowhere.
Have copied the code below. Would really appreciate some help. Thanks.

All <img> tags need to have an alt attribute that gives the text that would be read out by a screen-reader. The standard requires this to promote accessibility for the visually-impaired. The text for alt can be blank
(alt="") for images which are purely stylistic flourishes, but you're encouraged to use meaningful text where appropriate.

VALHAI-EPUB.EPUB IS VALID!
PREFLIGHT REPORT
Epubpreflight runs some of the same validation as epubcheck, but additionally checks for problems like very large file sizes that might affect some reading systems

Thank you so much, I really appreciate your taking the time to help me.